Health stocks were the sole losing group in the S&P 500 Index Tuesday after two biotechnology companies released disappointing study results. Data from Biogen Inc. and Alexion Pharmaceuticals Inc. showed that key trials of drugs failed -- sending the former down as much as 13 percent and the latter 12 percent. The health index doesn’t include Valeant Pharmaceuticals International Inc., which slumped as much as 22 percent after cutting guidance.

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